Copolyester-carbonate resins are well known commercially available materials which, due to their many advantageous properties are finding increasing use as thermoplastic engineering materials. Such copolyester-carbonates may be prepared by the reaction of a dihydric phenol, a carbonate precursor, and an ester precursor. The copolyester-carbonates exhibit high heat resistance, good dimensional stability, good tensile strengths, and good impact strengths. However, in certain applications the use of aromatic copolyester-carbonates is severely limited due to their relatively poor resistance to organic solvents such as, for example, gasoline, acetone, heptane, and carbon tetrachloride. The most significant effect of this poor solvent resistance is a loss in vital impact strength and also an increase in brittle type failure of parts fabricated from copolyester-carbonates which have been exposed to these organic solvents. Contact with such solvents may occur, for example, when parts are used under the hood of automobiles or near the gasoline filler ports thereof, or when solvents are used to clean or degrease stressed parts made from copolyester-carbonate resin.
In certain applications materials exhibiting both better organic solvent resistance and higher impact strengths than those exhibited by conventional copolyester-carbonates are required.
It is an object of the instant invention to provide copolyester-carbonate compositions exhibiting improved resistance to organic solvents such as gasoline, i.e., improved environmental stress crazing and cracking properties, and better impact strength than exhibited by copolyester-carbonate resins.